Hydraulic brake trailer system



Dec. 22, 1942. E. A. ROCKWELL HYDRAULIC BRAKE TRAILER SYSTEM Filed June 13, 1941 8 Sheets-Sheet l INVENTOR [HM ATT RNEY Dec. 22, 1942. E. A. ROCKWELL HYDRAULIC BRAKE TRAILER SYSTEM Filed June '15, 1941 J W VENTOR m AT RNEY 8 Sheets-Sheet 2 Dec. 22, 1942. E. A. ROCKWELL HYDRAULIC BRAKE TRAILER SYSTEM Filed June 15, 1941 8 Sheets-Sheet 3 I I a rlrlllllll INVENTOR W ATTORNEY gd'wa.

. 1942- E. A. ROCKWELL HYDRAULIC BRAKE TRAILER SYSTEM 8 Sheets-Sheet 4v Filed June 13, 1941 INVENTOR BY (2 a (a, ATTO NEY M i-W 8 Sheets-Sheet 5 Dec. 22, 1942. E. A. ROCKWELL HYDRAULIC BRAKE 'i'RKILER SYSTEM Filed June 13, 1941 "TNvENToR aimpww ATTORNEY 1 m I w g M? T p wwm Ill! I III kw M E, A. ROCKWELL HYDRAULIC BRAKE TRAILER SYSTEM- Dec. 22, 1942. v

8 Shets-Sheet 6 Filed June 13, 1941 !NVENTOR A M1 ATTORNE Dec. 22, 1942. E. A. ROCKWELL 2,305,638

HYDRAULICWBRAKE TRAILER SYSTEM Filed June 13, 1941 8 Sheets-Sheet 7 .Qm MM m \WWN WNH K -Dec. 22, 1942. a. A. ROCKWELL HYDRAULIC BRAKE ITRAILER SYSTEM Fi led June 1:5, 1941 8 Sheets-Sheet 8 lNVENTOR WHY ATTORNEY Patented Dec. 22, 1942 "OFFICE, I

HYDRAULIC BRAKE manna srsrniu Edward A. Rockwell, west Hartford, Conn. Application June 13, 1941, Serial No. 397,899

19 Claims.

My invention relates particularly to a system for the operation of. brakes on trailers, which is adapted to be used with automotive vehicles generally but has particular application to trailers operated in connection with trucks.

The object of my invention is to provide a trailer brake system adap ed to give exceptional performance and speed of action. A further obiect is to provide a system capable of being adapted for the operation of any dual-line vacuum trailer equipment. Another object is to provide a capable of operation with one or more of the power units disclosed in my copending application upon Power unit apparatus, Ser. No. 343,754, filed July 3, 1940. Again, a further ob- Ject is to provide trailer connections giving exceptional performance and which, if accidentally broken away, will automatically apply the brakes of the trailer when the latter breaks away. Furwhen using one of said power units and a poweroperated master cylinder on the trailer. also provided equipment brakes without requiring valves. Thesystem made in accordance with my invention is, furthermore, arranged to be interchangeable with difierent types of known systems applied to trailers. Further objects of my invention will appear from the detailed description of the same hereinafter.

le my invention is capable of embodiment in, many different forms for the purpose of illustration I have shown only certain forms thereof in the accompanying drawings, in which Fig. 1 is a schematic plan view of the simpler form .of my invention as applied to a main vehicle and trailer connected thereto;

Fig. 2 is a schematic for operating trailer the presence of relay shown in Fig. 2;

I have valve used in connection with both forms of my invention shown in Figs. 1 and 2;

Fig. 9 is an end-elevation of the power unit used on the main vehicle Fig. 10 is an end elevation taken at theother Fig. 4 is a vertical section of the same taken on line 4-4 of Fig. 3;

Fig. 5' is a plan view of the same;

Fig. 6 is' a vertical section taken online 6-6 of Fig. 4;

Fig. 7 is an end view of the adapter used in la- Fig. 8 is a longitudinal section of a brake-away 55 being accessible end of the same;

Fig. 11 is a longitudinal vertical section taken on line II-Il of Fig.9;

Fig. 12 is a plan view partly in section, taken 0 line I2-I2 of Fig. 9;

Fig. 13 is an end elevation of a modified form of said power unit, which may be used instead of the power unit shown in Figs. 9 to 12 and which is preferably used as part of the installation on the trailer;

Fig. 14 is an elevation taken at the other end of said power unit in Fig. 13;

Fig. .15 is a vertical section taken on line I5-I5 of Fig. 13;

Fig. 16 is a plan view partly in line Ii-IB of Fig. 13;

Fig. 17 is a diagrammatic view showing the relative sizes. of the power unit plungers used with the respective sizes 'of the master cylinder pistons and Fig. 18 is an elevation of the pedal and master cylinder used in connection with Figs. 1 and 2.

Referring to the first form of my invention shown in Figs; 1, 9 to 12 and 18, I have shown a pedal I mounted on a, lever 2 which is pivoted on a shaft 3 carried by a chassi I of an auto- A link 5 is attached to said lever 2 intermediate its ends so as to give any desired pedal ratio movement of .the pedal I to the brake-operating link 5. The said link 5 is pivotally connected to a piston 8 of a master cylinder I and which may be of any desired form, as for example of the type disclosed on the patent to Loughead, No. 1,707,063, granted March 26, 1929, or as shown in Fig. 4 hereof. The link 5 passes into the master cylinder through a collapsible rubber boot 8 so as to operate said piston Ii in a cylinder 9 beneath a storage chamber III having a vent II in a filler opening I2, the liquid to the chamber 9 through-an opening II in the retracted position of the piston 6. When the pedal I is moved downwardly the piston 6 is adapted to discharge the liquid of the master cylinder from a pipe I4 to an inlet opening I5 located in a removable fitting I6 screw-threaded in .a'casting I! at one end of the power unit, Fig; 11. Th fitting I I carries on its inner face a rubber seal I8 and the liquid from the fitting I6 is conveyed by a port I9 therein to a valve passageway 20 having. a plurality oi ionof the power unit section, taken on gitudinal channels 21 therein so as to communicate with a chamber 22 in said casting and thence initially to convey the liquid under manual pressure by a passageway 23 to an outlet port 24 which serves the purpose of delivering modulated hydraulic pressure manually, .or from the power apparatus hereinafter described, to the accessory to be operated, as for instance the wheel brakes of the automobile having the usual wheel brake cylinders for operating the brake shoes, for example as disclosed in my application aforesaid. It will be noted that the said casting l1 carries additional alternative outlet ports 25 and 26 constructed the same as the outlet port 24 except that they are located at different angles so that any one of them may be connected in themost convenient way to the line leading to the accessory to be operated. Furthermore, the said cast ing l1 supports an end cover 26a secured to an -outer shell 21 enclosing the parts of the power unit, by means of screws 26, the said shell 21 being supported in any desired manner, by straps 29 and 36 secured together by bolts 3|, spacing sleeves 32, nuts 33 and-lock washers 34, on the automobilechassis. Adjacent to the casting I1 there is provided a vacuum inletfitting 35 which contains a check valve 36, within a valve chamber 31 therein, adapted to seat against a bushing 38. In this way the vacuum, as for example by a pipe 36:: from an engine manifold 3617 or any other desired source, is supplied to the interior of the shell 21. Opposite to the vacuum inlet fitting 35 there is a vacuum trailer connection 39. The hydraulic liquid received from the line 14 also passes from the inlet opening l5 through a passageway 43 in the casting l1 and-thence by a pipe 44 into an opening 45 in a valve: casing 46 into which there is screw-threaded a iitting 41 for a pipe 46 which is connected by an angular pipe 46 into the side of a plunger housing 56 so as to communicate with a chamber 5| therein. The said chamber 51 also communicates with a passageway 52 adjacent to a valve seat 53 provided for receiving a conical end 54 of a bleeder valve 55 screw-threaded into the plunger housing 56. A plurality of transverse ports 56 extend through the reduced end of the bleeder valve 55 so as to communicate with a longitudinal pas-- sageway 51 in the bleeder valve, which is normally closed by a screw plug 58 held in position by a lock washer 59. When the plug 58 is removed and the valve 55 unscrewed to unseat the bleeder valve, the accumulated air is relieved through the passageway 51. The said plunger housing 56 supports in place a cover plate 66 by means of a nut 6|, the periphery of which rests upon a plurality of teeth 62 on the valve casing 46. The hydraulic liquid in the chamber 5| thus communicates with one face of a cylindrical plunger 63 having a rubber seal 64 on a reduced end thereof. As will be seen in Fig. 1'7, the plunger 63 may be made in several different sizes so as to be capable of being substituted in the apparatus with an appropriate size of plunger housing 66 so that by the increase in the area of the plunger 63 the power unit can be adapted to the operation of larger and heavier vehicles, such as trucks, in which a large volume of liquid is required for operating the wheel brakes thereon. In this Fig. 1'? there are illustrated, by way of example, three diameters of the plungers 63 with the relative diameters of the master cylinder pistons used therewith, it being understood that the pedal lever ratio for each set of diameters will be adjusted therewith to always obtain approximately the same ratio of force from the piston 9 to the force obtained from its plunger 63 in each of the three pairs of pistons and plungers. Unless this reduced area of the plunger 63, as compared with the master cylinder piston, were used the liquid from the master cylinder would be used up faster than desirable in obtaining an effective control. The other end of the plunger 63 carries a gasket 65 adjacent to a reduced end 66 thereon. It will be noted that the plunger housing 56 fits within and is fastened to the valve casing 46 by screws 61 and one end of the plunger housing 56 acts as a stop or support for an outlet valve 66 which is attached to the reduced end 66 of said plunger 63. The outlet valve 66 is arranged for movement within a chamber 69 in the valve casing 46, which communicates with a passageway 16 in the valve casing 46 and which passes through a supporting ring 1| fastened to one end of the outer shell 21 and to the valve casing 46 by screws 11a, thus giving access of the vacuum within the shell 21 to the outlet valve chamber 69. When the plunger 63 is moved forwardly by the liquid in the chamber 5| this causes the outlet valve 66 to seat against a diaphragm 12 of rubber or other suitable material, which is clamped at its periphery against one face of the valve casing 46 by a ring 13 having ports 14 therein. These ports 14 permit the passage of atmospheric air pressure to be received in the apparatus from a passageway 15 covered by a screen 16 which communicates with a chamber 11 filled with horse-hair and which is open to the air through the teeth 62 and the other periphery of the cover 66 spaced from the valve casing 46, as shown in Fig. 11. This atmospheric air is adapted, when the outlet valve 66 is seated, to enter beneath the periphery of an inlet .valv 18 which is normally seated on one face of the said diaphragm 12. This inlet valve 16 is supported on the inner periphery of a thin oxidized oil woven fabric ring 16 backed by a paper gasket 190, which latter is held in position against one face of the valve casing 46 by means of a clamping plate 66 and screws 6|. Furthermore, the said inlet valve 16 is clamped in position on the ring 16 by a clamping ring 62 and rivets 63 which pass not only through the inlet valve 16 but also through a ring 64 and a springsupporting ring 65 which is clamped thereby against one face of the diaphragm 12. It will be noted, also, that there are passageways 66 which pass radially from the outer portion of the inlet valve 16 inwardly to the inside of the ring 64 so as to communicate with a chamber 61 located'beneath the outlet valve- 66. In-this chamber 61 there is a spring 66 supported at one end upon the ring and at the other end upon the clamping plate 66 to normally force the inlet valve 16 to the left in Fig. 11. Also within the chamber 61 there isan inner spring 69, one end of which is seated on the said clamping plate 66 and the other end of which surrounds a small extension on the end of the plunger 63. The clamping plate 66 has perforations 66 through the same to permit the passage of the vacuum or air received in the chamber 61. Also passing through the clamping ring 66 and the valve casing 46 there is a passageway 9| for supplying modulated pressure for a trailer connection, also as an opening for the insertion of a lubricant. When the outlet valve 66 has been closed and the inlet valve 16 opened, the pressure of the atmospheric air is then received outwardly against the "II. On the other face of the on one iaceoiapiston lisoastomovethe same. This piston ing disc '4 ior holding in place a leather gasket II,- o'! right-angle cross-section, whichis held inner face of acylinder I. by a spring ring" which isin the term merely within the inner periphery oi the supporting ring piston ll there is a plate CI for holding in place a felt ring II which also bears on the inner periphery of the cylinder '00. The said plate It has a circular oil-set portion Ill around a plunger III on which both of the plates screws 2b provided with spacing-keepers 2c and nuts 2d so as to en'ectively clamp the disc I to the cylinder Within the end of the piston III there is an annular shoulder III, so is moved to the extreme shoulder III contacts with the fiange ill so as to pull-a valve member Ill, screw-threaded to the other end or the rod I I5. oi! its seat on the inlet fitting I. A spring Ill around a reduced end or the valve Ill, and which is supported at the otherend oi the spring upon a spider III carried on a shoulder III in the cylinder IIII, serving to hold the whole in the container 21, normally forces the valve III against its seat when not pulled away from the seat by the shoulder I II.

As angalternative power unit to the power unit lust described I may use. instead, the modified form of power unit shown in Figs. 13 to 16. This alternative form of the power unit is provided with the same connections to the master cylinder, wheel brakes and vacuum as in the form oi the power unit shown in the preceding figures., For this P e there is provided an inlet fitting Ill for the liquid from the master cylindenewhich communicates with sageway IIl'having a spring-pressed valve III therein arrangedto supply modulated hydraulic pressure to the wheel brakes from a port III, also a rod I22 and a plunger I23, all oi these parts being constructed substantially the same as in the form shown in the preceding figures. In this instance, however, the manual pressure liquid from the master cylinder, for applying the increased power, passes through an elbow I24 and thence through a pipe III to a fitting I" in a plunger housing The cylinder at issupported in place a valved pas-' carrieson oneiace-a clamp-' I21 having a bleeder valve casing III and thence to an elbow It! on the valve casing I", so as to admit vacuum thereto. The atmospheric air pressure is admitted to the outside of the inlet valve I" from a right-angle pipe M8 leading from a breather chamber I filled with horse-hair and carrying a peripherally vented cover plate I45. Opposite to the pipe I the valve casing I35 carries an opening I for supplying modulated other purpose. The admitted by the seating of the valve I and unseating of the valve I36,

ormed by a dishedcasing Illsecured by screws Illa to the valve casing III and having an annular flange ill adapted to be clamped to an annular flange III on the dished casing Illso as to support a flexible wall I" oi rubber or other material between said flange by means or screws Ill. The said wall In is in the form of a ring, the inner periphery 01' which is clamped between plates I and IE5 and on to the plunger I23. Around the plunger I28 there is a helical spring I", one end of which is seated against the plate I" and the other end against the dished casing III. A bushing I58 supports the free end of the plunger I23 and liquid is supplied to the wheel brakes through the passageway III when the power is being applied by the force of the plunger III to the right, in Fig. 15. It will be understood that in carrying out thisoperation, the rod In and the valve I III. which is supported in the same manner as in the form of the invention shown in Figs. 9 to 12, carries out the action in the same way as in said Figs. 9 to 12.

way valve Ill operated by a hand lever I65 and having three ports I", I" and Ill so as to either connect the ports I" and I" to the pipe I and a pipe I or so as to close theport Ill and connect the port I". and vent III with the pipe III in orderto Ill. This is arranged so that trailer brakes may be operated alone, when desired, when going down grade, by operating the hand lever I" to bring the ports I" and lllinto communication regulate the venting of the port with the pipe I69.

Said pipe I63 also leads to a hand valve I'll which is designed to cut oil the flow throu h said pipe when no trailer is being used. From this hand valve "I a flexible tube I12 leads to a; coupling I13 on a trailer chassis I14 where said coupling is attached to a flexible pipe I15 communicating with the rear end of a cylinder I16 having a piston I11 therein connected by a rod I18 passing through a rubber boot I19 to an arm I69 on a brake shaft I6I connected by arms I82 and links I63 to any usual mechanism for operating brake shoes on wheel brakes I34. It'will be noted that the cylinder I16 need not a matter of fact, this may be any usual type of dual-line operating brake actuating cylinder. In this instance it is comprised of a cylindrical wall I85 having heads I66 and I81 clamped together with bolts I33 which secure the cylinder to the trailer chassis I14 by means of brackets I99 and I99. The head I81 receives the endoi the pipe I16 and the head I86 receives a vacuum pipe I9I which is smaller in diameter than the pipe I15. The pipe I15 is relatively large in diameter so that there will not be any delay in the application of the atmospheric air through said pipe to the rear face of the piston 111, so that the brakes I94 will become set and receive at least some braking force when the manual force is being applied directly through the ports I9, 2i and 23 to set the brakes on the main vehicle. However, the pipe I91 is relatively small in diameter so as to give an appreciable lag in the releasing of the braking force on the trailer brakes I84 during the release of braking force by the piston 93 to the brakes of the main vehicle. This pipe I9I is connected by a valve coupling I92 which contains therein a helical spring I93 to normally open a valve I94 against which it rests, having a gasket I95 which seats on the end of the valve coupling I92. The valve I94 is adapted to move within a cylindrical valve housing I96 and has a longitudinal channel I91 to restrict th flow of vacuum communicating with a port I99 which passes transversely into a chamber I99 in the valve I94 communicating with a passageway 299 leading to an angle-fitting 29I having a'coupling 292 which, in case of accident, is arranged .to break the same as the coupling I13. The coupling 292 is connected by a flexible tube 293 leading to a hand valve 294 valve I1I which in turn communicates by'a pipe 295 to the opening 39 on the power unit.

The modified form of installation shown in Fig. 2 is installed on the main vehicle 4 in the same way as described in connection with the installation in Fig. 1, and the connections with the trailer chassis I14 are the same. The pipe I15 in this instance, however, leads to a power actuator 296 which in effect takes the place of the foot for the actuation of the master cylinder for the application of the brakes. This power actuator is comprised of a forward shell 291 and a rear shell 296 clamping between them a flexible rubber diaphragm 299 by means of bolts 2 I 9 passing through flanges 2H and 2I2 on said two shells. The diaphragm 299 has a thick inner periphery 2I3 which is clamped between two spring plates 2" and 2I5 secured on a plunger 2I6 by means of nuts 2I1'and 2I9. The plate 2I5 serves as the end support also for a helical springv 2I9, the other end of which rests against the shell 293. The plunger 2I6 extends into a bushing 229 within a cylindrical casting 22I within which it is sealed by means of a sealing ring 222 be provided with any valves and, as

constructed like the hand means of an end ring 224 and an angle ring 225 having a coil spring ring 226 between the same. The cylindrical casting 221 is secured to the shell 299 byscrews 221 having an interventin asket 228. The casting 22I, furthermore, serves as an adapter as it has a triangular face 229 provided with three screw holes 239 for receiving screws 23I having nuts 232 and lock washers 233 for holding the'actuator on a bracket 234 adapted to be secured to the chassis 114 of the trailer by means of a flange 235 and screw holes 236. Also, said screws 23I pass through ears 231 on a master cylinder 238. Said master cylinder 238 has a hydraulic cylinder 239 in which a piston 249 moves, provided with a recess 2 to receive the plunger 2I6, said piston 249 having a rubber seal 242 and said cylinder 239 having a ring 243 therein to act as a stop, held in place by a split ring 244. Above the cylinder 239 the master cylinder has the usual reservoir 245 and screw cap 246 as well as a vent 241, supported within a cover 249, and located between the said cap 246 and cover 249, secured in place by screws 249, there is a baiile 259 supported by a perforated ring 259a to prevent splashing. A port 25I makes a free connection between the reservoir 245 and the rear face of the piston 249, which also has transverse ports 252 to permit the movement of oil to the right while the piston 249 is being retracted. Before the piston 249 is being moved forwardly to the right oil enters by a port 253 from the reservoir 245 to the piston face. A rubber piston ring 254 is carried on the face of the piston 249 against which it is held by a helical spring 255, the other end of said spring being supported by a dished spring ring 256 which acts as Y a guide for a check valve 251 provided with a disc 259 which seats on a rubber ring 259 on one side of the retainer ring 256, the other side of said ring having a rubber ring 269 to support a small helical spring 26I carried by a retainer ring 262 mounted on the stem of the valve 251. At the end of the cylinder 239 beyond the valve 251 there is a chamber 263 having a screw plug 264, also a drain port 261 and an outlet port 268, which always retains a slight pressure, to connect the master cylinder to a flexible pipe 269 leading to the inlet port I I6 of a power unit 219 constructed like the power unit described in detail in connection with Figs. 13 to 16, and which is free from thrust with regard to the trailer chassis in the operation of the power unit and the operation of the trailer brakes from the power unit. The outlet or delivery opening I2I on this power unit leads by a flexible tube 21I to a. pipe 212 provided for operating brake cylinders 213 and wheel brakes 214 on the trailer. A flexible vacuum pipe 215 leads from a port 216 to a threeway fitting 211, the lateral port of which is connected to the check valve port I31 on the unit 219. Another branch of said fitting 211 goes to a flexible pipe 219 smaller in diameter than the pipe I15, which leads to the break-away valve I92.

In the operation of the trailer system, referring first to the form of the installation contained in Fig. 1, when the trailer is connected to the main vehicle and the valves Ill and 294 are open, the valve I64 is ordinarily kept in the position communicating with the pipe I69 and disconnected from the vent I61. At this time the vacuum is equalized in the power unit 21 and on both sides of the piston I11 and the brakes are to moveuntil they setby the manual are in snug position on the force, the trailer brakes will have been set and have some power applied thereto owing to the admission oi some air through the pipe I'll. Under these conditions, when the manual pressure is being applied initially by the However, the will not become seated under the insmallvariations in the vacuum. owing to the spring ill. Upon the further application 01' the at as the operation of the si l-id brake Shoes III and the modulated action ofthis air pressure,

hrough aboutby the movement of the pedal I will coordinately move the diaphragm 2|! so as pressure according into the brake cylinders 213 to operate the trailer brakes 214. As in the case of the form of my in controlling one of sai the operation of th applying device, said power-applying device comconnected thereto, the pipe which conveys the pressure not subjected to manual control comprising a relatively restricted means for impeding the flow of the fluid therethrough.

3. m combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two different pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means for controlling one of said pressures for the operation of the power unit and powerapplying device, the pipe which conveys the pressure not subjected to manual control including a check valve with a small portadapted to be mounted on the trailer, for impeding the flow of the fluid through said valve when unseated.

4. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two different pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means for controlling one of said pressures for the operation of the power unit and power-applying device, said power-applying device comprising a movable wall subject to operation by said pressures without control by valves between said power-applying device and the pressure lines connected thereto, the pipe which conveys the pressure not subjected to manual control including a valve with a small port, adapted to be mounted on the trailer, for impeding the flow of the fluid through said valve when unseated.

5. In combination, a power unit adapted to be applied to a main vehicle for the operation oi brakes thereon, sources oi. two different pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means for controlling one of said pressures for the operation of the power unit and power-applying device, the pipe which conveys the pressure not subjected to manual control including a check valve with a small port and break-away connection for impeding the flow of the fluid through said valve when unseated.

6. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two different pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located at a trailer connected to said vehicle and connected to said pipes, and manual means for controlling one of said pressures for the operation of the power unit and power-applying device, said power-applying device comprising a movable wall subject to operation by said pressures without intervening valves, the pipe which conveys the pressure not subjected to manual control including a valve with a small port and break-away connection for impeding the flow oi the fluid through said valve when unseated.

7. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two difierent pressures for operating said power unit, pipes leading from said power unit, a powerappiying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means for controlling one of said pressures for the operation of the power unit and power-applying device, the pipe which conveys the pres.-

sure not subjected to manual control including a valve and a pipe smaller in diameter than the pipe for the other pressure for impeding the flow of the fluid through said valve when unseated.

8. In combination, a power unit adapted to be applied to amain vehicle for the operation of brakes thereon, sources of two different pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means for controlling one of said pressures for the operation of the power unit and power-applying device, said power-applying device comprising a movable wall subject to operation by said pressures without intervening valves, the pipe which conveys the pressure not subjected to manual control comprising a relatively small-diameter pipe for impeding the flow oi the fluid therethrough.

9. In combination, a power 'unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two different pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means, comprising a hydraulic connection, for controlling one of said pressures for the operation of the power unit and power-applying device,-said power unit having pressure magnifying elements therein.

10. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two diflerent pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means, comprising a hydraulic connection. for controlling one of said pressur for the operation of the power unit and power-applying device, said power-applying device comprising a movable wall subject to operation by said pressures without control by valves between said powerapplying device and the pressure lines connected thereto, said power unit having pressure magnifying elements therein.

11. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two difl'erent pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means for controlling one of said pressures for the operation of the power unit and power-applying device, said power-apply device comprising a second power unit provided with pressure magnifying elements.

12. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two different pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, manual means for controlling one oi said pressures ior'the operation of the power unit and power-applying device, said power-applying device comprising a sec-- ond power unit provided with pressure magnifyfluid-operated power actu-. ator adapted to be mounted on the trailer, coning elements, and a nected for operation with the pipe containing a manually variable pressure and having a hydraulic connection from the actuator to said second power unit for operating the latter.

13. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two difierent pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, manual means for controlling one of said pressures for theoperation of the power unit and power-applying device, said power-applying device comprising a second power unit provided with pressure magnifying elements, and a fluid operated power actuator, comprising a movable wall and piston moved thereby, adapted to be mounted on the trailer, connected for operation with a manually variable pressure and having a hydraulic connection from the actuator to said second power unit for operating the latter.

14. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two diflerentpressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted 4 draulic line, an automotive the pipe containing to be located on a trailer connected to said vehicle and connected to said pipes, manual means for controlling one of said pressures for the operation or the power unit and power-applying device, said power-applying device comprising a second power unit provided with pressure magnifying elements, and a fluid operated power actuator, comprising a movable wall and a master cylinder containing a piston moved thereby, adapted to be for operation ing the latter.

15. In combination, a power unit adapted to be applied to a main vehicle for the operation of brakes thereon, sources of two different pressures for operating said power unit, pipes leading from said power unit, a power-applying device adapted to be located on a trailer connected to said vehicle and connected to said pipes, and manual means for controlling one or said pressures for the operation 01' the power unit and power-applying device, said power-applying device comprising a movable wall subject to normal operation by said pressures and a stiff spring associated with said wall for delaying the movement or said wall.

. said power unit,

' line so as to cut 01! the 16. In combination, a manually operated hydraulic line, an automotive accessory operatively connected to said line, a pneumatic motor connected to be operated by said line, a pressure increasing device connected to said motor, a valve operated as a result of the increase 01. pressure in said line so as to cut on the manual pressure to the accessory by the movement of said motor, and a trailer accessory-operating device connected to receive a pneumatic pressure from said motor.

17. In combination, a manually operated hyaccessory operatively connected to said line, a pneumatic motor connected to be operated by said line, including sources of two different wall operated thereby, a pressure increasing device connected to said motor, a valve operated as a result of the increase of pressure in said line so as to cut oil the manual pressure to the accessory by the movement of said motor, and a trailer accessory-operating device, including a movable wall, connected to receive a pneumatic pressure from said motor.

18. In combination, a manually operated hydraulic line, an automotive accessory operatively connected to said line, a pneumatic motor connected to be operated by said line, including sources of two different pressures and a movable wall operated thereby, a pressure increasing device connected to said motor, a valve operated as a result of the increase of pressure in said line so as to cut off the manual pressure to the acces'sory by the movement of said motor, and a trailer accessory-operating device, including a 'powerunit and a master cylinder for operating connected to receive a pneumatic pressure from said motor.

'19. In combination, a manually operated hydraulic line, an automotive accessory operatively connected to said line, a pneumatic motor connected to be operated by said line, including sources of two different pressures and a movable wall operated thereby, a pressure increasing device connected to said motor, a valve operated as a result of the increase 01' pressure in said manual pressure to the accessory by the movement of said motor, and a trailer accessory-operating device, including a power unit and a master cylinder for operating said power unit, connected to receive a pneumatic pressure from said motor, said power unit being constructed to be mountable on a trailer chassis without thrust therefrom with relation to the chassis in the operation or the power unit and the operation of the accessory rrom the power unit.

EDWARD A. ROCKWELL.

pressures and a movable 

